Low-grade B-cell lymphoma of mucosa-associated lymphoid tissue in the thymus of a patient with pulmonary amyloid nodules.

Low-grade B-cell lymphoma of mucosa-associated lymphoid tissue (MALT-type lymphoma) is a rare thymic tumor, with only seven previous cases described worldwide to date. We describe the only case to have presented with pulmonary amyloid nodules. A 63-year-old Japanese female was found to have an anterior mediastinal tumor and multiple bilateral pulmonary nodules during a medical check-up in 1990 followed by chest radiography and computerized tomography. Because the mediastinal tumor grew larger, she was referred to the National Cancer Center Hospital East and hyperglobulinemia was pointed out. The thymus was resected through median sternotomy and pulmonary nodules were also resected through left thoracotomy. The solid and nodular tumor with several small satellite extensions and cyst formation was completely confined to within the thymus and the resected pulmonary nodules consisted of solid masses with a rough surface. Histologically, monotonous medium-sized centrocyte-like cells occupied the medulla of the thymus and infiltrated Hassall's corpuscles (lymphoepithelial lesions) and the resected pulmonary nodules consisted of eosinophilic amorphous deposits which showed birefringence on Congo Red staining. Immunohistochemically, the tumor cells were positive for CD20 and CD79a. IgG and kappa light chain restrictions were also found in plasmacytoid cells in the tumor. Clonal rearrangement of the immunoglobulin heavy chain gene was demonstrated by polymerase chain reaction. We diagnosed this case as low-grade B-cell MALT-type lymphoma in the thymus and nodular pulmonary amyloidosis. Since the patient had only localized amyloid deposits in the lung far from the thymic malignant lymphoma and had high serum immunoglobulins, the pulmonary amyloid deposits might be derived from a circulating precursor associated with hyperglobulinemia.